Extracellular Ca2+ concentration takes a very important role in various living body functions including maintenance of life. Thus, serum Ca2+ concentration is strictly controlled within a very narrow range by many regulatory mechanisms.
Parathyroid hormone (PTH) is a polypeptide hormone produced in and secreted from the parathyroid glands and mainly regulates serum Ca2+ concentration. This PTH increases serum Ca2+ concentration by accelerating bone resorption and accelerating reabsorption of calcium in renal trouble. Increase of the serum Ca2+ concentration inhibits secretion of PTH, but on the contrary, decrease of the Ca2+ concentration accelerates secretion of PTH, so that it is considered that the serum Ca2+ concentration is controlled, in a sense, by a negative feedback mechanism.
Included in the hyperparathyroidism in which excessive secretion of PTH continuously occurs are primary hyperparathyroidism considered to be due to adenoma, hyperplasia, cancer which arises in the parathyroid gland itself and secondary hyperparathyroidism caused by chronic kidney disease and the like.
It has been reported that many patients with chronic kidney disease were simultaneously suffering from secondary hyperparathyroidism. Secondary hyperparathyroidism is one of the causative diseases of renal osteodystrophy including ectopic calcification, and considered to be a cause of the reduction of QOL of patients with chronic kidney disease due to bone fracture, bone pain and the like and of the death of patients with chronic kidney disease caused by a cardiovascular disease considered to be due to calcification in the cardiovascular system. Thus, the secondary hyperparathyroidism is a big problem in the clinical field, too.
In the secondary hyperparathyroidism caused by chronic kidney disease, excessive secretion of PTH is occurred from the reduction of serum Ca2+ concentration caused by the lowering of phosphorus excretion in the kidney and the reduction of active vitamin D. It is considered that this excessive secretion of PTH is continued and exacerbated due to further reduction of renal function, parathyroid hyperplasia, resistance of the PTH target organ and the like.
At present, vitamin D replacement therapy is mainly carried out as an internal therapy for the secondary hyperparathyroidism. However, since vitamin D preparations increase the serum Ca2+ concentration, they have an administration limit, so that it is not the state of being able to carry out sufficient treatment. Based on the above, concern has been directed toward the development of a secondary hyperparathyroidism treating agent which has high efficacy and does not increase serum Ca2+ concentration.
Calcium sensing receptor (CaSR) has been cloned initially as a G-protein coupled receptor (GPCR) which can sense extracellular Ca2+ in the bovine parathyroid (Non-patent Reference 1). CaSR has a function to change intracellular Ca2+ concentration by sensing extracellular Ca2+ concentration, and thereby to regulate production of molecules related to Ca2+ metabolism regulation, typified by PTH. As a fact to support this, many reports have been published stating that activation mutation or inactivation mutation of human CaSR is a cause of familial hypercalcemia or hypocalcemia. In addition, reduction of sensitivity of the parathyroid gland for Ca2+ has been observed in both primary and secondary hyperparathyroidism.
It is considered that an agonistic regulatory agent of CaSR reduces PTH without increasing serum Ca2+ concentration, by increasing Ca2+ sensitivity through its direct action upon CaSR of the parathyroid gland. Recently, it has been reported that an agonistic regulatory agent of CaSR, cinacalcet, has an activity to inhibit PTH secretion by increasing Ca2+ sensitivity of CaSR through its direct action upon CaSR of the parathyroid gland (Non-patent References 2 and 3). Cinacalcet is expected as a new hyperparathyroidism treating agent which may be used jointly with a vitamin D preparation as an already known therapeutic means, a Ca2+-containing phosphate binder which has been used for the purpose of treating hyperphosphatemia and the like.
However, it has been reported that cinacalcet has a strong activity to inhibit CYP2D6 which is one of the subtypes of cytochrome p450 (CYP). This CYP2D6 also has an important role in the metabolism of various drugs used in the clinical field. Since cinacalcet inhibits CYP2D6, there is a danger of causing drug-drug interaction (DDI) by changing pharmacokinetics of a drug through the delay of metabolism of a drug metabolized by CYP2D6 (Non-patent Reference 4). Based on the above, concern has been directed toward the development of a strong CaSR regulatory agent free from CYP2D6 inhibitory activity.
It is considered that mRNA of CaSR is expressed in various tissues including the kidney and parathyroid gland, in addition to the parathyroid gland which is a main PTH secreting tissue and takes various physiological roles.
It is expected that an agent which regulates CaSR antagonistically or agonistically (CaSR regulator) could become a therapeutic agent of various diseases including bone disease and diseases of upper and lower digestive organs (Non-patent References 5 and 6), diabetes mellitus (Non-patent References 7 and 8), hypo-/hyper-function of pituitary (Non-patent Reference 9) and the like, in addition to the aforementioned hyperparathyroidism.
Regarding the CaSR regulator, there are two reports of the following Patent References 1 and 2.
In the Patent Reference 1, compounds represented by the following formula (A) and formula (B) comprising a broad range of compounds are disclosed. However, as Ar, R and R3, there is no disclosure on pyrrolidine which is a characteristic of the invention.
(In the formula, Ar, R and R3 represent the following meanings.    Ar: a hydrophobic substance.    R: hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, indenyl, indanyl or 2-, 3- or 4-piperidyl.    R3: a monocyclic or bicyclic aryl or cycloalkyl having 5 or 6 ring constituting atoms, which may be substituted.See said reference for other signs.)
A compound represented by the following formula (C) is disclosed in the Patent Reference 2 published after the priority date of the instant application. However, in the compound represented by formula (C), amino group is directly linked to a nitrogen-containing ring.
(See Said Reference for the Signs.)
In addition, Patent Reference 3 describes that compounds represented by the following formula (D) including pyrrolidine derivatives are effective for migraine, as an agonist of 5HT1-like receptor. However, there are no descriptions on their efficacy for CaSR regulatory activity and hyperparathyroidism.
(The M in the formula represents a residual part of azetidine, pyrrolidine or piperidine ring. See said reference for other signs.)
Non-patent reference 1: Brown et al., Nature, (England), 1993, vol. 366, p. 575-580
Non-patent reference 2: Cohen et al., Current Opinion in Pharmacology, (Holland), 2002, vol. 2, p/734-739
Non-patent reference 3: Joy et al., The Annals of Pharmacotherapy, (USE), 2004, vol. 38, p. 1871-1880
Non-patent reference 4: Sensipar™ (cinacalcet HCl) Tablets), [online], 2004, FDA [retrieved date [Mar. 28, 2005], internet, (URL:http://www.fda.gov./cfer/foi/label/2004/21688-Sensipar-1bl.pdf).
Non-patent reference 5: Jeannine et al., The Journal of Clinical Investigation, (USA), 1997, vol. 99, p. 2328-2333
Non-patent reference 6: Cheng et al., The American Journal of Physiology-Gastrointestinal and Liver Physiology, (USA), 2002, vol. 383, p. G240-G250
Non-patent reference 7: Bruce et al., The Journal of Biological Chemistry, (USA), 1999, vol. 274, p. 20561-20568
Non-patent reference 8: Straub et al., The Journal of Biological Chemistry, (USA), 2000, vol. 275, p. 18777-18784
Non-patent reference 9: Emanuel et al., Molecular Endocrinology, (USA), 1996, vol. 10, p. 555-565
Patent Reference 1: International Publication No. 94/18959
Patent Reference 2: International Publication No. 2005/115975
Patent Reference 3: International Publication No. 96/04274